Pituitary borty.—The process just described is the connecting link between the brain and that glandiform body, the pituitary gland or hypopkysis. This body, situate in the sella Turcica, is of a rounded form, longer in the transverse than the antero-posterior direction, concave on its superior surface, into which the pituitary process is inserted. It is surrounded by dura mater, which projects over it, leaving . an opening for the passage of the infunch bulurn.
The pituitary body is about six lines in its transverse diameter and three lines from before backwards: its weight, including the infundi bulum, is about eight grains. It consists of two lobes, one anterior, the other posterior. The former is kidney-shaped and lodges the latter in the notch of its posterior edge. In point of size the anterior lobe is nearly double the posterior.
The colour of the posterior lobe is lighter than that of the anterior, and resembles that of the grey matter of the brain.
This body is proportionally larger in early life than at the later periods, and it is certainly more developed in the lower mammalia than in man. It is very large in fishes, and pro bably reaches its maximum of size in that class of animals.
The structure of the pituitary body resem bles very much the grey cerebral matter. It is composed of large nucleated vesicles, sur rounded by a granular matrix, with bundles of white fibrous tissue. This fibrous tissue either forms an essential element in its constitution, or accompanies the bloodvessels which are found in it in great nunibers. Its substance is soft, but not so soft as the cerebral matter, and when pressed between the fingers is re duced to a greyish pulp, like the substance of an absorbent gland in an early stage of suppu ration.
Earthy concretions have been occasionally but very rarely found in the pituitary body. This circumstance, its colour, its glandiform character, and its extra-cerebral situation in connexion with the third ventricle, give it a certain degree of analogy to the pineal body. But in this latter nervous fibres have been found, of which I have failed to discover any trace in the pituitary, nor is the pituitary body connected to the brain by fasciculi of fibres as the pineal body is. The use of both is equally involved in ohscurity; but from their con stancy it may be argued that their function is not unimportant. It has been supposed that
the pituitary body is a large ganglion belong ing to the sympathetic system : this opinion, however, wants the all-important foundation of anatomy to rest upon, inasmuch as we find that the body in question is devoid of the ana tomical characters of a ganglion. It-may w th more propriety be classed with the glaads without efferent ducts; and from its numerous vessels, and its close relation to part of the venous system within the cranium, it May be connected with the process of absorption or re moval of the effete particles of the brain.
Of the ventricles of the brain.—The third ventricle results from the apposition of the lateral halves of the brain along the median plane, and the lateral ones from the folding inwards, above and below, of the convoluted surface of each hemisphere. They must not therefore be regarded as cavities hollowed in the substance of the bmin : on the contrary, their walls must be viewed as part of the cerebml surface, and the eminences which project from them as convolutions. The car pom striata and optic thalami are from their structure entitled to be considered in this light, and still more the hippocampi, which, how ever, are somewhat complicated by the addi tion of the layers of white matter derived from the fomix.
The distinction between the lateral and the middle or third ventricle results from the de velopment of the corpus callosum and of the form; which form horizontal strata by which the ventricles are closed in above ; and the extension of the anterior pillars of the fornix downwards, and the close application of the free margin of the body of the fomix to the optic thalami, assign more complete limits to the third ventricle.
The fourth ventricle is also evidently formed by the lateral adaptation of the symmetrical halves of the medulla oblong-ata. The iter is obviously a continuation of it closed behind by the quadrigeminal bodies and their con necting fibres. 'This ventricle remains open in the embryo, uncovered by any portion of the encephalon until the full developement of the cerebellum causes it to extend over it.